Each year in Portland there is a sand-sculpting fundraiser in the central square called "Yoshida's Sand in the City." The money goes to support "Kids on the Block" a volunteer puppet program that goes into schools to teach children positive messages about themselves and others.
Businesses pay money to get a sandbox and in exchange get some advertising. Around the sand there are some booths with information about Kids on the Block, and a few other organizations have minor crafts projects for kids.
While the art is always cool, there's not really a whole lot of community building happening. The event is free and in the middle of downtown Portland, so it's nice to stroll by, but there's no reason to interact with other people. There is a sandbox for children to play in and make their own castles (kids get all the fun), but it's not much. Of course, it's probably a good bonding exercise for the company employees who make the sculptures.
Take in comparison two fountains located in downtown Portland which are permissible to enter. Both are always present, unmonitored, and free. Architecturally, they're fun to play in.
As compared to the tiny sandbox above, the fountains attract people of all ages. From children and grandparents to young lovers, these fountains become gathering and relaxing points for the city on a hot summer day.
(it should be noted that this fountain continually changes its patterns throughout the day to reflect the tempo of the city)
You can see more pictures of the sand sculptures here.